Time Travel

And we probably won't in our lifetime.

 

In terms of relativity, it's a simple concept, with an ironic twist:

1) Mass and Energy are different forms of the exact same thing...like water and ice.
2) Massless particles MUST move at the speed of light (ironic, since energy increases and thus so should mass)
3) Anything with mass CANNOT move at the speed of light.

So in a particle physics sense, going back in time almost implies that one has 'negative mass.' I don't know if this seems absurd, but perhaps it should be.

Has anyone ever worked with a 'spacetime diagram' ? Where you plot the speed of light, and show how quantities 'limit' towards it...here's a simple one:



The blue line represents the set of events that one witnesses while moving at constant velocity. Here's a more descriptive version, known as 'the light cone.'



If anyone's interested, I'll explain some stuff about relative simultaneity in regards to this second picture (ie. can cause precede effect? When are two events simultaneous?)

 

thats some crazy stuff Mike, and it seems pretty cool to. But like you said, mass can't travel at the speed of light, unless its 'negative mass'. So, how would you get 'negative mass'? Can you? Is it possible?

 

EDIT 2: Sorry, I forgot in the previous post (and in this one) to rectify the irony in the mass-energy thing...Mass and Energy are different forms of the same thing right? Like water and ice, as I mentioned...thus, if you want 'as much water as possible' you melt all the ice, right? To move at the speed of light, an infinite amount of energy is required...thus the amount of mass is pushed to zero, since all of it is converted into pure energy. So yes, the amount of 'mass + energy' goes arbitrarily large...but it's all energy, so the object must be one of pure energy, ie. a massless particle (such as light).

That's the misconception I wished to address but forgot, sorry. So that might answer Mythril_Roxas's question about negative mass: it can't really go below zero to give that extra bit of energy...simply because the energy is already 'infinite.' Once you've melted all your ice to make the maximal amount of water, you can't have 'negative ice' by melting the remaining 'nothing,' and gaining water.




Disclaimer: The following descriptions occur in what's known as Minkowski Spacetime...this is basically a (widely accepted) model for our universe, which behaves as we can observe. It has 4 dimensions, x,y,z and t...or more precisely, 'ct' (where c is the speed of light). This is just for mathematical purposes, because we can define what's known as a 'metric' on this space defined by dp^2 = dx^2 + dy^2 + dz^2 - cdt^2...but this isn't such an important detail, so if you don't know what a metric is, don't sweat it. The important point is: This is a four dimensional space...the two dimensional diagram above is a REPRESENTATION of four dimensions...so it's kind of like we squish the x y and z spatial dimensions into one, and time is the other...that's why instead of dealing with distances, we deal with 'how vertical' a line is.

Also note: Points on the above diagram represent EVENTS...not locations, or times, but both: Locations at a given time.

EDIT: Also note that this is a model for spacetime...but it is a mathematical model nonetheless. Even though my explanations will be a bit vague (ie. 'somewhere in the upper yellow triangle') if you know the distances and times of things, you can actually calculate exactly where they lie, with respect to each other.

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The solid yellow lines represent particles (events) moving away from 'Event P' at the speed of light. The slower you get, the more 'vertical' you get...ie. if you're looking at someone say, turning a TV on, watching for an hour, and then turning it off, the TV didn't move (for all intents and purposes), the two events lie somewhere on the y-axis, the solid white, vertical line through Event P.

If we let turning on the TV be Event P, then the act of turning off the TV will lie ABOVE Event P, in the "Absolute future" of P. Conversely, if we let turning off the TV be event P, then turning on the TV is a direct cause of it, and thus is in the "absolute past" of event P.

If the events move...like say you take a drink in the kitchen, then after an hour you walk to the washroom...then if we let the act of drinking be Event P, then using the washroom will lie somewhere in the upper yellow triangle (but NOT on the solid white line).

Now, for the solid yellow lines...suppose Event P is turning on a flashlight...the light travels at c, and will 'see' lots of events at lots of different locations. The set of these events represent those lines...but as noted in other points, c is a 'speed limit.'

So the idea is, if two events are arbitrarily far apart at a given time, then they could not possibly have influenced each other. Namely, if one event happens, and light can't travel fast enough to trigger the other event, then nothing possibly could...these 'not possible' event relationships represent the points in the blue 'side' triangles.

Now in case I didn't explain well enough (it's much easier if I could do so on say, a blackboard), the take home points are as follows:

-Event P is a 'chosen' event we're looking at...let's say waking up in the morning.
-The lower yellow triangle in the above diagram is the set of all events that culminate in event P (note that the triangle 'stretches on forever' downward)
-The upper yellow triangle is all events that are CAUSED by event P...so everything you do that day, and all the consequences, including sleeping and waking up the next day and so on.
-The blue sections are events which you could not possibly have influenced...because they're 'too far away' from each other. Namely, LIGHT can't even move from one event to the other, quick enough. In the case of this diagram, Event P and Event Q do NOT have a cause and effect relationship.


This is the idea behind relative simultaneity...effect can never precede cause...but when you move at different speeds (as I'll explain in a later post), you can actually make non-causal relationships occur simultaneously! (and simultaneous events occur non-simultaneously)

Let me know if this is clear enough...I'm going to do a bit of a 180 when I talk about "simultaneous" events (which will ultimately link back to this topic). I don't want to post too much at once as it gets a bit confusing.

 

thats was cool





i actually learned something from all that. Thanks Mike!!
I get what your saying. So you've further proven my statement, we can't time travel, or at least not with the technology we have now.

 

Actually, it almost implies that we could never possibly do it, regardless of technology...

However, if our notion of 'physics' or math is incorrect in some way (as I've mentioned in other threads), this is meaningless...

So to reiterate the point I've been trying to make in the other threads, you really do have to put your 'faith' in science to believe it is sound. The fact that with our science time travel seems absurd, doesn't mean it really is...maybe there's some 'trick' that allows us to overcome the energy problem, by looking at some other quantity, fundamental to energy itself (as one idea).

String Theory anyone?

(And if anyone is still interested in simultaneity...the idea is that if I see two things occuring simultaneously, then if you ran by at some arbitrarily large speed, you'd see them occuring at different times. If anyone's interested I can explain why that is)

 

Could something like Anti-Gravity Matter allow us to Time Travel? Its virtually mass less, correct?

 

Your teacher's a 'foolish believer of science' as I call them. Not that he's foolish, but that he's accepted a convention, which is neither proven nor even feasible, given other scientific 'data' (such as the Big Bang) as being the be-all and end-all of everything. Yes, IF energy is never created nor destroyed, then time travel raises some problems...but if we're wrong, why is it a problem? (Big Bang suggests that it's certainly not the whole truth, if you believe in that stuff (which the people who think science is sound, do)).

Conservation of Energy, and Conservation of Momentum are two things which have never been proven...merely 'observered' and over many years never had an observed contradiction.

Anti-Gravity Matter...Not quite sure what you mean there. Dark Matter?

I'm not a big fan of the whole Dark Matter hypothesis. The way it seems to me, is that scientists posed a theory, and then tried to explain simple concepts, namely they tried to answer the question: Why is the universe accelerating outwards? There should only be an attractive, gravitational force (pulling it together), and failed to explain it. So they go "Hmm...maybe there IS something out there! Let's call it dark matter, and it's something we can't detect...oh yeah, let's pretend we know it exists too, because we can pump out a mathematical formula."

It's impressive that they can put out a formula that works, but does that make it true? In the words of Stephen Hawking, "Who cares if it's true, so long as it's reproducible, and can make predictions." (But of course, the assumption that it's true is faulty)


Now that I think about it, what you might mean is something like 'anti-matter' in the following sense: Gamma rays can produce electrons and 'positrons,' whichf when they collide, explode into nothing (and energy). This anti matter, in theory (I think...not 100% sure here) experiences time in reverse. So it's almost like, say if we're going 299,999,999 m/s (1 m/s less than the speed of light) the corresponding anti-matter particle would move at 300,000,001 m/s...the speed of light acts as a kind of 'mirror' through which time reverses direction (as light does in a normal mirror). The anti-matter particle looks to us, like it move 299,999,999 m/s...but time to it, is actually occuring in reverse.

The idea is, if something is 'experiencing time backwards' it takes an infinite amount of energy to 'slow down' to the speed of light, just as it takes us an infinite amount of energy to speed up to it.

I'm not as confident in my knowledge on this stuff, I might have just made up a lot of it right now, haha...seems to make sense though...but I'm not sure if 'anti-matter' has negative mass or not. I guess it kind of does.

(I'll get to the other stuff in a little bit)

 

I just know that Nicola Tesla was a mad scientist in the late 1800's to early 1900's, and invented the radio. Later in life he talked about something called Anti-Gravity Matter, and no one believed him. The government took a bunch of things out of one of his secret vaults he had, possibly things that could "prove" his thoery on AGM, but the govz got it now, and they supposedly killed him later in life. He was one of those people who 'never gave up'.

 

Not to take the easy way out, but here's a wikipedia article that talks about all this stuff...but the underlying principle is that this is all made up...no evidence to support any of the ideas. It has to do with all kinds of stuff, from negative mass, to imaginary mass (ie. imaginary numbers), to other things.

Exotic matter - Wikipedia, the free encyclopedia

 

Lulz, this is impossible. So die your butts trying, pathetic scientists! lolz

 

you dont think we can acheve time travel I think we will I mean if we acheved flight something that the human body isnt capeble of doing yet we did it

 

controlling flight is different than controling time.

 

time insnt even real we fabrecated it to give ourselfs a sence of orginization

 

Ill search for some theories explaining why time travel isn't possible.

 

Time travel is a bunch of lie, if you could go to the prehistoric with different outfit, that's ruin the future, i mean, the prehistoric people saw you and thought you're a god. Then they keep worshipped you and what happened next? The regional will be ruined if God didn't send He's prophet.

 

I dont think that would happen at all

 

There is a difference between 'time' as an object, and 'time' as a measurement. We have invented the concept of a 'second' or a 'minute' as a way to explain the passing of time...and yet no matter how we describe it, time still passes.

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What is time, in its purest sense?

Time is no different than motion...that is, it's motion in a 4th dimension...just like walking to the left is motion in the first 3 dimensions.

This is a very real quantity that is inherent in our universe (or so it appears). We choose to measure distance in meters (or inches, light years etc) but these don't capture what motion actually is.

This is exactly like time...we can make stopwatches to help us agree on the amount of time that passes, but this quantity does not capture what time itself is:

Time is motion...no different from moving up or down, or left or right. The only difference is that we do not control this motion. Everything in our universe is 'plunged' into constant motion in this dimension. That's all it is...

Intuitively, one might think of a 'slideshow' where each instant in time is a snapshot of the universe. Then the next instant (however close together they are) is the next snapshot.